Boris Johnson could face trial over claims he was lying when he said the UK gave the European Union £350 million a week during the 2016 referendum.

The frontrunner in the Tory leadership race has been accused of misconduct in public office after making the claim during the campaign, following a private prosecution by campaigner Marcus Ball.

A date has not yet been set for a court hearing, but could come after the Tory leadership contest has concluded – meaning Mr Johnson, if he wins the race, may face trial as prime minister.

His first appearance at magistrates’ court could occur during the contest.

A source close to Mr Johnson said the prosecution was “nothing less than a politically motivated attempt to reverse Brexit and crush the will of the people”.

“The claimant has openly admitted that his plan is to overturn the referendum via a legal challenge and he clearly intends to try and undermine the one man who can truly deliver Brexit.

“The decision to issue a summons is extraordinary, and flies in the face of hundreds of years of British democratic tradition.”

The decision to summons the former foreign secretary was criticised by Tory Brexiteer Jacob Rees-Mogg, who said it was a “troubling” abuse of process.

He told the Press Association: “It is trying to use the courts to achieve a political end which, I think, is neither right or proper. This is involving the courts in something that is not their area.

“We need courts and politicians to respect each other, and it is an abuse of process, and a troubling one. It has been brought by people who are resentful of the referendum result.”

And Conservative former cabinet minister and barrister David Mellor said the ruling was a “deplorable absurdity”, and that courts should not adjudicate on what politicians do during election campaigns.

Jacob Rees-Mogg said the case had been ‘brought by people who are resentful of the referendum result’ (Kirsty O’Connor/PA)

“I imagine there will be no shortage of senior judges who will feel acutely embarrassed about this,” he told the Press Association.

“Politicians at election times exaggerate, and say things that may or may not be true, and it’s the electorate, not the courts, who should decide whether they are reliable or not.

“This is a bad day for British justice. But probably, contrary to the wishes of those who have crowdfunded this nonsense, a big boost to Boris. Is that what they really intended? Nutty, nutty, nutty.”

Health Secretary Matt Hancock, who is also vying for the top job, said: “However people voted in the referendum, we shouldn’t have courts judging on political debates.

“Let’s have robust debate to test arguments – and keep courts out of politics.”

However people voted in the Referendum, we shouldn’t have courts judging on political debates. Let’s have robust debate to test arguments – and keep courts out of politics

Lawyers representing Mr Ball lodged an application to summons Mr Johnson to court, claiming he had deliberately misled the public during the Brexit referendum campaign in 2016 and then repeated the statement during the 2017 general election.

In a written decision, District Judge Margot Coleman said: “The allegations which have been made are unproven accusations and I do not make any findings of fact.

“Having considered all the relevant factors I am satisfied that this is a proper case to issue the summons as requested for the three offences as drafted. The charges are indictable only.

“This means the proposed defendant will be required to attend this court for a preliminary hearing, and the case will then be sent to the Crown Court for trial.

“The charges can only be dealt with in the Crown Court.”

In her ruling, Ms Coleman said: “The applicant’s case is there is ample evidence that the proposed defendant knew that the statements were false.

“One example is given that in a televised interview in May 2016 the proposed defendant stated, ‘we send the EU £10 billion per year’ and that therefore he knew that the £350 million per week figure (£20 billion per year) was incorrect.”

A section of the judge’s ruling included Mr Johnson’s position, which described the application as a “(political) stunt”.

His position in summary said: “This application is brought for political purposes. The position presented to the Court is that this is a disinterested attempt to improve the standards of political debate.”

It added: “The application is a (political) stunt. Its true purpose is not that it should succeed, but that it should be made at all. And made with as much public fanfare as the prosecution can engender.”

The £350 million figure was emblazoned on the red campaign bus used by Vote Leave during the referendum, with the slogan saying “We send the EU £350 million a week let’s fund our NHS instead”.

Lewis Power QC, representing Mr Ball, told Westminster Magistrates’ Court last week: “Democracy demands responsible and honest leadership from those in public office.

“The conduct of the proposed defendant Boris Johnson was both irresponsible and dishonest. It was, we say, criminal.”